Deducing details about Apple’s A6X processor

Apple promises double the CPU and graphics performance over the A5X, but how?

As usual, Apple didn't share many specifics about its new A6 "Extreme" (A6X) processor, which powers the fourth-generation iPad. However, by looking at Apple's claims that it's "twice as fast" as the A5X-powered third-gen iPad, it may be possible to deduce what's inside.

According to Apple, the A6X processor "delivers up to twice the CPU and graphics performance of the A5X chip." In other words, the dual-core CPU can process data twice as fast as the dual-core 1GHz, Cortex A9-based A5X. It can also churn through OpenGL triangles and textures at twice the rate of the PowerVR SGX543MP4 in the A5X. So how did Apple do that?

Looking at CPU power for the moment, we already know that Apple designed a custom ARM-based core for the A6. Running at 1.2GHz in the iPhone 5, two A6 cores run twice as fast as two 800MHz A5 cores in an iPhone 4S.

However, the A5X in the third-gen iPad was clocked at 1GHz. That means Apple is clocking the A6X higher yet. Given that architectural improvements account for some of the speed increase, Apple only had to clock the iPhone 5 at 150 percent to achieve double the compute performance of the iPhone 4S. With this in mind, we believe Apple is clocking the A6X's CPU cores at 1.5GHz.

Examining the GPU is slightly different. Apple already jammed four SGX543 GPU cores into the A5X in order to achieve performance parity with the two SGX543 GPU cores in the A5 chip that powers the iPad 2. The extra GPUs were needed just to keep up with the 2048×1532 pixel Retina display, so these did not offer any graphics performance improvement. However, Apple says that the A6X pumps pixels twice as fast.

Apple could be using a newer-generation PowerVR core, but that appears to be very unlikely. Only one announced processor is known to use a PowerVR Series6 design, and it won't even begin sampling until 2013. Given that Apple just released the A6 a month ago, we're confident Apple is still using the same SGX543 core.

Here's what we know about the PowerVR SGX543 core's performance: it scales almost linearly with the number of cores and clock speed. So to double the performance, Apple would either have to double the number of cores to eight or double the clock speed of each of the four cores. Apple says that the A6X has "quad-core graphics"—the same as the A5X—so Apple clearly boosted the clock speed. Since the GPUs in the A5X were clocked at 250MHz, we believe that Apple has clocked the SGX543 cores at 500MHz.

Given the significant boosts in clock frequency—150 percent for the CPU cores, and 200 percent for the GPU cores—you may be wondering how Apple can still promise a 10-hour battery life. After all, the iPad still has the exact same 42.5Whr battery, but the processor is twice as powerful. The power savings come from the same place as we saw in the iPhone—Apple moved from a 45nm process to a more power-efficient 32nm process. Instead of keeping performance the same and decreasing the iPad's thickness and weight, Apple instead chose to double its performance without sacrificing all-day battery life.

Of course, we won't know how accurate our educated guesses are until one of the new iPads can be thoroughly benched, and the A6X's architecture is analyzed by the likes of Chipworks. However, we feel confident suggesting Apple has mated two A6 ARM cores running at 1.5GHz with four PowerVR SGX543 cores running at 500MHz. Given the performance results we saw with the iPhone 5, we expect the updated iPad will remain at the top of the tablet performance heap for some time.

How do you figure? Remember, the A6X is likely on the more power-efficient 32nm process, rather than the 45nm process of the A5X. A6's clock speed in the iPhone 5 is up over the iPhone 4S without making that device too hot.

You forgot to discuss one of the other major differences between the A5 and the A5X, the number of memory channels. I'd assume the A6X will continue to have 4 32bit channels just like the A5X and will probably use the same slightly faster ram that they use on the A6 in the iPhone 5.

Is 500MHz a realistic clock for the SGX543MP4 to be operating at? I tried looking for other products and couldn't see any using it go that high.

Was thinking the same. I think if it was that easy, a lot of other phones would be doing it, or we would have at least seen it somewhere surely?

I'm not doubting the theory for getting to a simple 2x clock bump making the 2x performance boost claimed, I just think the significance of this if being true has been severely underplayed/under-discussed here.

I wouldn't expect the GPU's to be clocked higher than 400 Mhz. Most of the performance gains in the GPU area likely stem from the vastly improved memory controller and higher clock memory. To be honest, I'm surprised that Apple didn't add any additional GPU cores. If they were comfortable with a relatively large A5X die in the iPad 3, they'd be able to live with a similarly large die for the follow up. It is driving a 3 megapixel display where all that GPU processing can be put to use. Perhaps they're too memory bandwidth limited for large GPU gains to be noticeable?

CPU clock speeds may even top out higher than 1.5 Ghz. The iPhone 5 can clock all the way up to 1.3 Ghz in small bursts but cruises at 1 Ghz for most common operations. Clocking all the way up to 1.8 Ghz might be possible for short bursts with a more common 1.5 Ghz speed under load.

I'm wondering if the amount of memory has changed. The silence on this spec leads me to believe that nothing has changed in this area so I'm expecting 1 GB.

I'm still grumpy they didn't reduce its weight. First thing I thought when I held the 3rd-gen iPad was that it's too heavy.

The weight increase relates to the Retina display being a power hog and thus requiring a bigger battery to retain the 10 hours of battery life.

Seeing as the Retina is still there and no big improvements in battery technology have been made since Spring, the only option to reduce weight would have been using the A6 design to not make a faster chip, but one that uses less power at the same performance. But the SoC uses very little power compared to the Retina display, they would not land in iPad 2 territory weight-wise.

So Apple had two possible sales pitches:

1) The new iPad, it's a bit lighter than before, but not much.2) The new iPad, twice as fast!

With such performance claims, in such a short amount of time since the launch of A5X, I'd generally agree with your assessment of a smaller node and faster clocks. I would also put a vote in towards faster memory/more bandwidth. The A5X was a large chip, and while less than ideal in this segment (size/yield issues, heat, etc), it was a safe way to launch the Retina iPad until the A6X could be properly prepared. In reality, if the A6X would have been ready 6 months ago, we might have seen a Retina iPad that was not as thick as the A5X model. Rather than redesign the whole works this go around, it appears that Apple is tossing in extra performance instead. Seems like good business.

The iPad wont slim down to its iPad 2 weight & thickness until we get to IGZO displays, presumably in 2013. IGZO can cut display power consumption anywhere between 50-90%. IMO, we wont see Macbook Airs with retina displays until we can get IGZO screens made at 11" and 13" at costs that are in line with its price point.

"we expect the updated iPad will remain at the top of the tablet performance heap for some time."

It won't. Google's Nexus 10 tablet should surpass it in both GPU performance (72 Gflops for Mali T604 vs 64 Gflops for the overlocked SGXMP4), but especially in CPU performance. I've seen Samsung's Exynos 5 Dual score under 700ms in Sunspider, with double the score in the V8 and Octane tests (compared to A6, which has just 20% lower CPU performance than A6X).

The GPU difference needs to be balanced with the fact that the Nexus 10 supposedly has 1.3 times more pixels but only 1.12 times more powerful a GPU, meaning in practice the iPad will still generally have a more powerful GPU.

The Exynos 5-dual was tested at 1.7GHz, and will likely be clocked lower when put into a tablet (it's the same process and very similar technology to the iPad, in a system with more pixels, a more powerful GPU, and in the same size/weight range, so it probably will be clocked at 1.4GHz or even lower).

In all previous iterations of iOS vs Android, an 1GHz A5X was competitive with a 1.2GHz Krait or Exynos; it will be interesting if the same is true here when the A6X is even more aggressively clocked to 1.5GHz or so.

"we expect the updated iPad will remain at the top of the tablet performance heap for some time."

It won't. Google's Nexus 10 tablet should surpass it in both GPU performance (72 Gflops for Mali T604 vs 64 Gflops for the overlocked SGXMP4), but especially in CPU performance. I've seen Samsung's Exynos 5 Dual score under 700ms in Sunspider, with double the score in the V8 and Octane tests (compared to A6, which has just 20% lower CPU performance than A6X).

From a technology standpoint you are probably right.

From a marketing standpoint, I doubt it'll matter much. There appears to be very little incentive to craft applications to a particular platform in the Android arena. (i.e., if it displays OK on a phone, well, that's kinda good enough.) It's ben discussed here before; there are simply too many variants to support.

In the IOS bag, it's different. The apps (to the buying public) are crafted. God help the rest when you throw in all the apps that have been tweaked for retina displays.

By the time the Android camp has adjusted to this state of affairs, well, we'll be talking about different tech.

Switch from ITO to IGZO and you'll see a reduction in LED count by 1/3 and therefore necessary battery (maybe a quarter), which then translates to a thinner, lighter design, besting even the iPad 2.

FYI...

IGZO is not actually a replacement for ITO (a transparent conductor used for the electrodes on the liquid crystal cells). Rather, it is a replacement for amorphous silicon used to make the thin-film transistors in the backplane. IGZO has a much higher carrier mobility than a-Si, which allows you to make the transistor smaller without degrading it's performance. That in turn lets more light through the screen, allowing for backlights with less power consumption. (There are already backplanes made with low temperature polysilicon (LTPS), which has an even higher carrier mobility than IGZO, but the process used to deposit LTPS is much more expensive and is hard to scale up to larger sized panels.)

Depends on whether you buy into marketing numbers or wait until actual test results can be parsed out in an unbiased manner. Your call.

We know very well from iPhone 5 benchmarks that the A6 CPU is twice as fast as the A5X CPU. Therefore, it isn't a stretch to say the A6X will also be twice as fast as the A5X. The only part that we are waiting for is the graphics, but as the author pointed out there are two easy ways that could have been accomplished. I would bet that Apple is telling the truth.

So Apple effectively made the ipad 3 obsolete overnight? LOLOLOLOLOLOLOLOLOLOL

Trollery aside… yes. We bought my dad an iPad 3 just last week. The rumors of an upgraded full size iPad hadn't really stirred up yet. He is returning it for an iPad 4. 2x cpu and gpu performance + a better FaceTime camera is nothing to sneeze at.

I didn't put much thought into, just struck me as a dumb name when I was reading the article.

It is. The AirPort Extreme got criticism for its name when it came out. Quartz Extreme probably did too, though I think we were all so happy that Apple was working on OS X's slowness that we didn't care too much about the silly name.

I didn't put much thought into, just struck me as a dumb name when I was reading the article.

It is. The AirPort Extreme got criticism for its name when it came out. Quartz Extreme probably did too, though I think we were all so happy that Apple was working on OS X's slowness that we didn't care too much about the silly name.

I'm sure neither got criticized as much as the iPad... or even the iPod. It seems to me, the more the name of an Apple creation gets criticized, the more successful it'll be.

The iPad wont slim down to its iPad 2 weight & thickness until we get to IGZO displays, presumably in 2013. IGZO can cut display power consumption anywhere between 50-90%. IMO, we wont see Macbook Airs with retina displays until we can get IGZO screens made at 11" and 13" at costs that are in line with its price point.

I suspect that price isn't much a factor for moving retina displays into the MacBook Air. Currently prices for the high resolution panels are higher and to accommodate them, Apple has literally split its product line up in two: MacBook Pro and the MacBook Pro w/ Retina Display. Why not a MacBook Air w/ Retina Display? I can even see Apple tolerating a 1 mm or 2 mm chassis height increase to squeeze in the higher resolution panel.

We bought my dad an iPad 3 just last week. The rumors of an upgraded full size iPad hadn't really stirred up yet. He is returning it for an iPad 4. 2x cpu and gpu performance + a better FaceTime camera is nothing to sneeze at.

We bought my dad an iPad 3 just last week. The rumors of an upgraded full size iPad hadn't really stirred up yet. He is returning it for an iPad 4. 2x cpu and gpu performance + a better FaceTime camera is nothing to sneeze at.

What does your dad do with all that CPU and GPU performance?

Presumably he looks at web pages that are rendered much more quickly (amongst any number of other possibilities).